This invention relates generally to identification documents and a method for making such identification documents. More particularly, this invention relates to a method for securing an image by means of graphical anti-counterfeiting means and to a method for securing an identification document with such graphical anti-counterfeiting means. The invention also relates to a secure identification document that allows detecting either a fraudulent modification of the existing personalization or a fraudulent falsified document.
Identification documents, with or without chip, such as driving licenses, identity cards, membership cards, badges or passes, passports, discount cards, banking cards, money cards, multi-application cards, and other papers of value; and security documents such as bank notes are widely used. Because of the value and importance associated with each of these data carriers, they are often the subject of unauthorized copying and alterations, and forgeries.
To prevent such activities from being carried out on these data carriers, different types of visual and touchable security features have been added to data carriers. One of these security features is a pattern, which is made with wavy lines that draw pre-determined motifs. Such pattern is superimposed on the personalization data, for example photography, and is commonly known under the name “guilloches”. FIG. 1 show an illustration of such a guilloche pattern 10 superimposed onto the photography 12 of the owner of an identification document.
However, the shape of such pattern is predictable because the same on all the documents of one batch. Consequently, it is very easy for infringers to scan the pattern and to reproduce it on a blank document on which a fraudulent photograph has been printed, in order to manufacture completely falsified documents.
To prevent such counterfeiting, one solution consists in taking into account the personalized data of the owner to define a personalized pattern for each document. However, with such a solution, the policemen can no more do a first verification by simple visual inspection, and they have to rely on a separate dedicated reader device. Consequently, such a solution is time and cost consuming.
Another solution to prevent counterfeiting consists in computing the grey level of the original image, at the location of the targeted guilloche pixel, in order to reverse the luminosity of this guilloche pixel compared to the original image so that the guilloche pixel becomes perceptible to naked eye. FIG. 2 shows a schematic guilloche line 110 inserted into part of an image 100, in which the luminosity of target pixels 111, 112, 113 has been changed to form the guilloche line 110. In this figure, the guilloche line uses a grey scale that contrast highly with the background. For example, the guilloche pixels appear clear 111 on a dark area 101 of the picture, and dark 112, 113 on a clear area 102, 103 of the picture. However, this approach does not protect blank documents against illicit personalization as there is no way, with or without reader, to detect whether the security pattern (guilloche) was generated using the correct algorithms and has the correct grey level. In fact, an infringer can scan the guilloche pattern and apply it on a fraudulent image by reversing the luminosity of the target guilloche pixel. Furthermore, even if the guilloche pattern is now perceptible and resistant to image degradation, the contrast may be too high and it can affect the image perception because it does not take into account the Human Visual System. The Human Visual System is defined as the way people perceive images, i.e. the process involving not only the eye but also the image processing parts of the brain.
Considering the above, the invention aims to improve the existing prior art solutions by enabling a first visual inspection of only one predictable pattern shape, a reader based detection of illicit personalization, and by using knowledge of Human visual system to improve the visual perception of the inserted security pattern.
Thus, a first technical problem intended to be solved by the invention is to provide a method for securing a first image by a security pattern image overlapping the first one, wherein each image is defined by a plurality of pixels, said method enabling to insert security pattern by using knowledge of human visual system in order not to alter the visual perception of the first image, to use only one predictable security pattern so that a first visual verification remains possible, and to detect an illicit personalization by means of a dedicated reader.
A second technical problem intended to be solved by the invention is to secure an identification document holding an identification image by inserting a security pattern image into the identification image, said method preventing a subsequent fraudulent modification of the personalization to be made, which is easy to detect by using a dedicated reader, and preventing the manufacturing of a completely falsified identification document.
Another technical problem intended to be solved by the invention is to provide a method for verifying the authenticity of an image secured by means of a security pattern image inserted into it, said method enabling to detect all types of fraud, either a completely falsified image or an image having been subsequently modified.